Add Chrono.h - std::chrono support header
Summary:
std::chrono mostly covers the functionality of llvm::sys::TimeValue and
lldb_private::TimeValue. This header adds a bit of utility functions and
typedefs, which make the usage of the library and porting code from TimeValues
easier.
Rationale:
- TimePoint typedef - precision of system_clock is implementation defined -
using a well-defined precision helps maintain consistency between platforms,
makes it interact better with existing TimeValue classes, and avoids cases
there a time point is implicitly convertible to a specific precision on some
platforms but not on others.
- system_clock::to_time_t only accepts time_points with the default system
precision (even though time_t has only second precision on all platforms we
support). To avoid the need for explicit casts, I have added a toTimeT()
wrapper function. toTimePoint(time_t) was not strictly necessary, but I have
added it for symmetry.
Reviewers: zturner, mehdi_amini
Subscribers: beanz, mgorny, llvm-commits, modocache
Differential Revision: https://reviews.llvm.org/D25416
llvm-svn: 284590